The present invention relates to a drill tool for making a drilled hole, especially a hole with an undercut.
For making of drilled holes with undercuts located at the base of the drilled hole a drill tool or bit is used whose drill head has lateral cutting elements projecting from the drill tool shaft or drill head . This type of drill tool can be clamped in a hammer drill machine and used for making drilled holes and the undercut in them. An insertion depth stop, which extends from the drill tool shaft, limits the insertion depth of the drill tool. A collar cast onto or formed on the shaft can act as the insertion depth stop. An elastic ring-like damping element made of plastic can be slipped over the collar to protect the wall surface. An enlarged portion is provided on the drill tool shaft between the drill head and the insertion depth stop, which contacts on the drill hole wall. This enlarged portion acts as a pivot bearing for reaming out the undercut. The pivoting of the drill tool in the drill hole is possible and is achieved because the drill tool shaft can be narrowed or tapered uniformly from the enlarged portion toward the drill head and the insertion depth stop.
In drilling downwardly and in drilling holes which are long, the drilling cuttings from the drilling cutting grooves build up behind the enlarged portion between the drill tool shaft and the drill hole wall that the drill tool is stuck in a clamped position in the wall or is released only with great difficulty. Because of that, neither removing the drill tool from the drilled hole to clear out the drill cuttings nor a pivoting of the drill tool to make the undercut is possible.